Bug #15731: Wrong evaluation of many keyword default arguments in 2.3 - 2.5

• Status: Closed
• Assignee: -
• Target version: -
• ruby -v: ruby 2.5.3p105
• Backport: 2.4: REQUIRED, 2.5: REQUIRED, 2.6: DONTNEED

[marcandre (Marc-Andre Lafortune)]

I don't know if it's worth fixing at this point, but we found a strange bug with evaluation of default keyword arguments when there are many of them (more than 32).

def foo(
  k0: puts(0), k1: puts(1), k2: puts(2), k3: puts(3), k4: puts(4),
  k5: puts(5), k6: puts(6), k7: puts(7), k8: puts(8), k9: puts(9),
  k10: puts(10), k11: puts(11), k12: puts(12), k13: puts(13), k14: puts(14),
  k15: puts(15), k16: puts(16), k17: puts(17), k18: puts(18), k19: puts(19),
  k20: puts(20), k21: puts(21), k22: puts(22), k23: puts(23), k24: puts(24),
  k25: puts(25), k26: puts(26), k27: puts(27), k28: puts(28), k29: puts(29),
  k30: puts(30), k31: puts(31), k32: puts(32), k33: puts(33)
  )
  k33
end

puts "No params:"
foo # Should print 1 to 33

puts "Only k33 param:"
foo(k33: 1) # Should print 1 to 32

puts "Only k32 and k33 params:"
r = foo(k32: 1, k33: 1) # Should print 1 to 31 and return 1

puts "Result: #{r.inspect}"

Ruby 2.4:
last case is wrong. It prints 1 to 33 instead of 1 to 31 and returns nil instead of 1.

Ruby 2.5:
same result for last case
first two cases evaluates the default exactly the wrong parameters: those that are given and not for those not given. So it prints nothing and 33 respectively, instead of 1 to 33 and 1 to 32!

Ruby 2.6:
results are ok

This strange behavior disappears with fewer keyword arguments.

[marcandre (Marc-Andre Lafortune)]

Edits:

Print 1 to ... => Print 0 to ...
Ruby 2.4 bug => Ruby 2.2/2.3/24 bug
Ruby 2.6 ok => Ruby 2.1 and 2.6 ok
We => Me and Maxime Lapointe

[fcheung (Frederick Cheung)]

FYI, I see the bad behaviour on 2.6 and master too. I think the root of the issue is here: https://github.com/ruby/ruby/blob/master/vm_args.c#L405 - it uses a bitmask to capture which kwargs have been passed, and that bitmask is stored in a 32bit int. Changing that constant to 64 (and the integers used to store the bitmask to 64 bit ints) make your examples run ok, although it is of course just pushing back the issue to when you have 64 kwargs

[nobu (Nobuyoshi Nakada)]

• Is duplicate of Bug #14373: Methods with more than 32 keyword arguments with default values have some of the arguments set to default despite being passed in. added

[nobu (Nobuyoshi Nakada)]

• Status changed from Open to Closed
• Backport changed from 2.4: UNKNOWN, 2.5: UNKNOWN, 2.6: UNKNOWN to 2.4: REQUIRED, 2.5: REQUIRED, 2.6: DONTNEED